 There are three main steps of PCR which are called as denaturation, second step is annealing and the third step is extension which is also called as elongation. So PCR consists of three main steps, first one denaturation in which the double standard DNA is converted into single standard. Second step is annealing where the primers they bind to the single standard DNA and the third step is extension which is also called as elongation. In this step DNA polymerase extends the newly strand that is complementary to the template strand. The first step in case of PCR is called as initialization step. So this step consists of heating the DNA which is double standard when we heat the DNA between 93 degree centigrade to 96 degree centigrade the double standard DNA is converted into single standard DNA. So usually during the first step which is called as initialization step at this step DNA or the tubes which are kept in the PCR machine they are kept for approximately 1 to 10 minutes. So this is the first step in case of PCR reaction. So once the initial denaturation has been done, so first regular cycling of the PCR starts and the first step is again denaturation. During the first cycling step of the PCR which is denaturation at this step DNA is kept at 93 degree centigrade but there can be some variation it can be 93, 94 or 95 degree centigrade for 20 to 45 seconds. So during this step the double standard DNA separates into single standard DNA. So this step is actually when we have to convert double standard DNA into single standard DNA and that step is called as denaturation of the DNA. The second step of the PCR is called as annealing. At this step which is usually at the temperature of 40 degree centigrade to 65 degree centigrade there can be variation between the annealing of different primers at some of the primers they can bind at 40, 45 and usually maximum temperature of the annealing is kept up to 65 or in some cases it can be 67. So we can say that there is some variation in case of annealing temperatures. So annealing temperature because during the previous step the DNA which was double standard has been converted into single standard during this step of annealing the primers which are also called as oligonucleotides they will bind to the single standard DNA. This is the third step of the PCR which is called as extension. In some literature or in some books it is called as elongation. So elongation is the step where DNA polymerase adds the nucleotides and new strand is formed that is actually complementary strand of the template DNA. The polymerase has the optimum activity between 70 degree centigrade to 80 degree centigrade but most of the time or in most of the cases of PCR commonly or commonly 72 degree centigrade is kept at which there is an optimum activity of the DNA polymerase. So this is the third step of the PCR which is called as extension. Extension is done with the help of DNA polymerase and mostly the temperature is kept 72 degree centigrade. This is the last or the final extension during the PCR because sometimes there are unfinished strands of the DNA so a final extension is given that can be one that can be one to seven minutes so that if there is any unfinished products that can be finished. So during extension DNA polymerase that have added the DNTPs to the newly synthesized strand so extension is the third step and once extension is done there is the final elongation or the final extension. At this extension 70 to 74 degree centigrade it can be for 5 to 15 minutes but in most of the cases it is performed at 72 degree centigrade for 5 to 10 minutes. Final whole temperature this is the last step of the PCR that is for a short term storage of the amplified product because the PCR has been finished once there is a final elongation so at the end for a short term storage of the amplified product this step is added which is called as final whole temperature.